Sparkling wines

Sparkling wines are those which contain carbon dioxide, providing bubbles and effervescence. For some sparkling wines, CO2 pressures as high as 600 kPa atmospheres can be reached (by comparison, the pressure inside a can of soda pop is less than 200 kPa).Although sparkling wines are made throughout the world, there are several manufacturing methods that are used to produce the CO2, and these methods define, to a certain extent, the type of sparkling wine being produced.

Clearly, the most well known sparkling wine is Champagne, which is traditionally made, not surprisingly, via the Champagne method. For other sparkling wines, CO2 is introduced by other methods, as described below. It is worth mentioning that Champagne, like Parmesan and Roquefort cheeses, enjoys a protected status in the European Union. Only wine produced in the Champagne region of France— just to the southeast of Paris—and made according to the centuries-old process and aged in the caves in that region can be called Champagne. All other carbonated wines, regardless of how CO2 is introduced, must be referred to as sparkling wine. In contrast, wine makers in the United States, which are under no obligation to follow EU rules, can label any sparkling wine as a champagne.

The manufacture of sparkling wines starts out no differently than other wines. The main difference is that at some point carbon dioxide is introduced into the "still" (i.e., not carbonated) wine.There are four possible ways to perform this step. The first is to simply add CO2

directly to the wine, followed by bottling. This is not unlike soda pop production and is definitely the most economical means.At about $5 a bottle,this "champagne "although bearing little resemblance to the real thing, is certainly the favorite of budget-minded celebrants.

The other processes all involve a second ethanolic-CO2 fermentation performed by yeasts (the exception, however, are those wines that contain CO2 as a result of the malolactic fermentation). However, in contrast to the primary fermentation, which is done in ambient atmosphere (i.e., open), the second fermentation occurs in an enclosed environment such that the CO2 is trapped and becomes supersaturated in the wine. One seemingly simple way to initiate such a fermentation is to stop the primary fermentation before all of the sugar has been fermented, and then to bottle the wine and allow the remaining sugar to be fermented by the residual yeast. The difficulty with this method is that stopping and starting the fermentation is not always so easy. Still, this method has long been practiced in France, Germany, and Italy.

Rather than rely on the endogenous sugar and yeast from the primary fermentation, an alternative and more common means of initiating the second fermentation involves the direct addition of an additional source or "dose" of sugar, as well as an inoculum of yeast, to the still wine.The yeast need only ferment a modest amount of substrate (usually sucrose) to generate enough CO2 to make the wine bubbly. The secondary fermentation can be performed either in enclosed vats or directly in bottles. For either method, however, there remains the problem of the residual yeast, which, if not removed, will make the wine cloudy or turbid. Sparkling wines, especially champagnes, are prized for their absolute clarity and perfect appearance.Thus, removing the yeast following the second fermentation is absolutely necessary. Several methods have been devised to perform this step.

In the bulk or Charmat method, the second fermentation occurs in a pressurized vat, then the wine is filtered to remove residual yeasts and filled into bottles under pressure. In the transfer process the wine is placed into thick-walled bottles, sugar and yeasts are added, and the bottle is corked.After the second fermentation in the bottle is complete, the wine is transferred into tanks, filtered to remove yeast and then re-bottled. In the Champagne method, the process is similar to the transfer system, except that no transfer occurs. Rather, the second fermentation occurs in the bottle, where the wine remains. How then, if the wine does not leave the bottle, can it be clarified and made free of residual yeasts? The answer to this question and other unique features of Champagne manufacture are described below.

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